This invention relates generally to data and information communication systems and their operation, and, more particularly, to communications networks, including a Fiber Channel network. Even more particularly, the present invention relates to a streaming method for Fibre Channel network devices that provides the ability to handle read/write requests from multiple Fibre Channel hosts that are larger in size than the available memory in a SCSI router by streaming data outward to the network device as data is received from a Fibre Channel host, or vice versa.
In a Fibre Channel-to-SCSI router architecture, one SCSI initiator (interface), such as a SCSI router, can speak to multiple SCSI targets on behalf of many Fibre Channel (xe2x80x9cFCxe2x80x9d) initiators (hosts). The SCSI router serves as an interface to efficiently manage commands and communications between the FC initiators and the SCSI targets. On the SCSI side of the network, each of the SCSI targets is only aware of the SCSI router interface connection to which it is directly attached, and likewise each of the FC hosts sees only the SCSI router as a target. Neither the FC hosts nor the SCSI targets are aware of targets or initiators, respectively, on the other side of the SCSI router to which they are connected.
In a Fibre Channel-to-SCSI network, a SCSI router provides a pass-through data management role. For example, when a Fibre Channel host issues a command to a SCSI target the SCSI router receives the command and forwards it to the target. To the FC host, the SCSI router is the target, and the data management role provided by the SCSI router is transparent to the host. Similarly the SCSI target on the other side of the SCSI router sees the SCSI router to which it is attached as the initiator of the command. The data management role provided by the SCSI router is likewise transparent to the SCSI target.
As part of their data management role, SCSI routers in a Fibre Channel-to-SCSI network receive read and write commands from FC hosts. The amount of data contained in these read/write commands can be more than the capacity of the memory in the SCSI router. For example, a write command might consist of a one megabyte (xe2x80x9cmegxe2x80x9d) stream of data while the SCSI router may have only a half meg worth of memory buffers to receive, store and forward the write command.
In a typical existing SCSI router implementation, the SCSI router saves the data and routes it to the target device. If the target device is a sequential access device, such as a tape backup, this can result in rejection of the command and possible corruption of the data if the available memory in the SCSI router is insufficient to capture all the data. Existing router architectures typically have no mechanism for dealing with this situation. Existing SCSI routers likewise have no mechanism available for informing the FC host of the available memory size prior to the host issuing the command. Although there are some existing SCSI router implementations that provide for initial discovery of available memory by the FC host, these methods are inefficient, slow and expensive to implement.
Existing systems and methods for managing data flow in a Fibre Channel-to-SCSI network typically store all the data associated with a command in the SCSI router memory before forwarding the data to the SCSI target device. Once the storing event is complete, the write or read to the SCSI target is performed. Therefore, even when there is enough physical memory present to handle a read or write command, current systems provide relatively low performance and efficiency because available memory buffers are tied up until the read or write command is complete. These memory buffers cannot be used by other FC hosts until the current read or write command has completed execution. Current systems therefore both tie-up available memory resources for a longer time than necessary and limit Fibre Channel network performance, even in situations where the SCSI router memory is enough to handle the data associated with a read or write command.
In a Fibre Channel-to-SCSI network the possibility also exists that a SCSI target may be incapable of receiving data at the same rate that a FC host is providing the data. For example, during a write event a Fibre Channel host may provide a larger data stream than the intended SCSI target is currently capable of receiving. In such a case, the SCSI router interface attempts to match the data transfer rates between the Fibre Channel host and the SCSI target or risks corruption and possible loss of data. In currently existing Fibre Channel-to-SCSI data management methods and systems if the available memory buffer space is insufficient to provide a delay to match the data rates between the FC host and the SCSI target, the command may be aborted and the data being transferred may be corrupted or lost. Currently existing systems and methods do not have the capability to hold-off the FC host until enough memory buffer space becomes available.
Additionally, because currently existing Fibre Channel-to-SCSI network data management systems and methods typically store an entire read or write command data before forwarding the data to or from the SCSI target, subsequent requests to use the memory cannot be satisfied until the prior command is complete. In a situation where sufficient memory is unavailable to process additional commands from a FC host (or from a different FC host), currently existing systems and methods reject the command and the command is lost unless it is reissued by the host.
In prior art systems, a read/write command requiring a data transfer larger than the available buffer memory size would typically get rejected. This could result not only in corruption or loss of data, but in a failure of the FC host or the SCSI target involved in the data transfer. This is not a good situation because it means that the SCSI router is incompatible with the FC host. Especially in the case of a sequential access target device, the backup or transfer in progress could fail and the target device might have to be reset. Prior art systems dealt with this problem by limiting the size of read/write commands. This solution resulted in reduced network performance.
Furthermore, in the case of a sequential access target device, it is not possible to break-up a write or read command into discrete pieces that can be written to the target at different physical locations. For example, if a FC host issues a 1,024K write command to a sequential access device, the sequential access device will write the data to a physically continuous 1,024K memory block. The sequential access target device expects to subsequently read the data as a 1024K continuous block with a single end-of-record indicator at the end of the read. If an end-of-record indicator were present anywhere else in the data, a sequential access device would fail and the operation aborted. For this reason, a read/write command to or from a sequential access device in a prior art system had to be stored completely in the available SCSI router memory and then transferred to the target device so as to be physically written in a continuous manner.
Prior art Fibre Channel-to-SCSI data management methods and systems implemented within a SCSI router also require larger amounts of memory to deal with the limitations inherent to sequential access devices. This results in a correspondingly higher cost.
Therefore, there is a need for a streaming method and system for Fibre Channel network devices that addresses the performance limitations arising in known such methods and systems. In particular, a need exists for a FC streaming method and system that provides the capability for processing read/write commands that are larger in size than the available SCSI router memory without the adverse effect in network performance and possible data loss problems occurring in known Fibre Channel-to-SCSI architecture command processing methods and systems.
A still further need exists for a streaming method and system that avoids the complexity and cost inherent to currently existing command processing methods and systems that require FC hosts to determine the available memory buffer size before sending a read or write command.
A further need exists for a streaming method and system for Fibre Channel network devices providing the capability to deliver data to a target device while concurrently receiving data from a host (or vice versa) so as to provide an in-and-out data stream between the host and the target device through a SCSI router.
A still further need exists for a Fibre Channel network streaming method and system having the capability to process any size data transfer between a Fibre Channel host and a target device.
An even further need exists for a streaming method and system providing the capability to match the data transfer rates between a Fibre Channel host and a target device so as to avoid the data corruption and loss problems of currently existing command processing methods and systems. Such a streaming method and system can hold-off initiator data transfers until the necessary memory becomes available to store the data and forward it to a lower data rate capable target device.
A further need exists for a streaming method and system having the capability to process read/write commands from multiple FC hosts to multiple target devices.
An even further need exists for a streaming method and system that can queue commands from one or more Fibre Channel hosts within the SCSI router interface such that subsequent commands are not lost while awaiting execution of a prior command.
A still further need exists for a streaming method and system that provides command processing in a Fibre Channel-to-SCSI router interface without the cost and physical memory requirements of current command processing methods and systems while providing increased performance and efficiency.
In accordance with the present invention a system and method for processing commands to target devices through a SCSI router in a Fibre Channel-to-SCSI network is provided that substantially eliminates or reduces disadvantages and problems associated with known such systems and methods, including the problems of limited network performance, loss of data in certain applications and general application failures. More specifically, the present invention provides a system and method for processing commands to network target devices through a SCSI router in a Fibre Channel network having a plurality of Fibre Channel hosts. In the case of a sequential access target device, the method includes the steps of, in the SCSI router, initializing one or more memory modules into preset size memory buffers and receiving a command from one of the plurality of Fibre Channel hosts. The SCSI router can be any kind of router that can serve as a Fibre Channel-to-SCSI interface in a Fibre Channel-to-SCSI architecture, such as a Crossroads Systems, Inc., of Austin, Tex., Model 4100 or 4200 SCSI Router. The Fibre Channel network can be a Fibre Channel arbitrated loop or switch network or other network topology.
If the command received requires a transfer of data larger than a threshold size, the method of this invention streams the data to the target device by first determining if a preset size memory block is free. The memory block itself can be comprised of one or more memory buffers. If the memory block is free, the method of the present invention requests a preset size data block from the Fibre Channel host that issued the command. Otherwise, the method of this invention holds-off the Fibre Channel host by waiting until the preset size memory block is available and then requesting the data block from the Fibre Channel host. The SCSI router receives a data block from the Fibre Channel host that issued the command and stores the data block in a FIFO queue. The steps of determining if the preset size memory block is free and requesting a data block from the Fibre Channel host are repeated until an initial number of data blocks are received and stored in the FIFO queue.
The system and method of this invention forward the command and the first of the data blocks received and stored in the FIFO queue to the sequential access target device (xe2x80x9cSATDxe2x80x9d). The SATD requests the next data block from the FIFO queue. Subsequent data blocks in the FIFO queue are forwarded to the SATD upon request until a trigger number of data blocks remain in the FIFO queue. The SCSI router maintains this trigger number of data blocks in the FIFO queue until all the data is received from the Fibre Channel host. The SCSI router maintains the trigger number of data blocks by simultaneously receiving additional data blocks from the Fibre Channel host and storing them in the FIFO queue and forwarding the topmost data block in the FIFO queue to the SATD.
The SATD requests additional data blocks from the SCSI router until it has received all of the data associated with the command. The SCSI router maintains a data block available to forward to the SATD by requesting a data block from the FC host to replace the topmost data block in the FIFO queue as the topmost data block is forwarded to the SATD.
If the command received from the FC host requires a transfer of data smaller than the threshold size, the method of this invention stores all of the data in one or more memory buffers as they became available and simply forwards the data to the SATD. The streaming capability of this invention is not required in such a case.
An alternative embodiment of the method and system of this invention provides for the streaming of data to a random access target device (xe2x80x9cRATDxe2x80x9d). In this alternative embodiment, an individual command for each block of data transferred is forwarded to the RATD. Unlike a SATD, a RATD is capable of writing and reading data as discrete packets stored in physically separated locations on the recording media. These data packets can be recombined into an original continuous piece of data larger than the individual component data packets. SATDs on the other hand, require that all data that is part of a single read or write command be written as a physical continuous piece of data on the recording surface.
The streaming method for Fibre Channel network devices of this invention can also be implemented in a Fibre Channel-to-SCSI network having more than one SCSI router. Similarly, the method of this invention can also be implemented in a Fibre Channel-to-SCSI network having multiple targets and multiple FC hosts connected through one or more SCSI routers. In the case of a Fibre Channel network having multiple SCSI routers, the method of this invention can be implemented separately within each of the SCSI routers.
A technical advantage of the streaming method of the present invention is the capability for handling read/write commands to a target device that are larger in size than the available memory in a SCSI router without a decline in network performance and the possible data loss problems occurring in known Fibre Channel-to-SCSI architecture command processing methods and systems.
Another technical advantage of the present invention is the capability to stream data to a target device while avoiding the complexity and cost inherent to currently existing command processing methods and systems that require a Fibre Channel host to determine the available memory buffer size within a SCSI router before sending a read or write command.
A further technical advantage of the present invention is the capability to deliver data to a target device while concurrently receiving data from a Fibre Channel host device (or vice versa) so as to provide an in and out data stream (streaming) between the Fibre Channel host and the target device through a SCSI router.
A still further technical advantage of the present invention is the capability to match data transfer rates between a Fibre Channel host and a SCSI target device so as to avoid the data corruption and data loss problems of currently existing command processing methods and systems. Such a streaming method and system can provide the capability to hold-off initiator data transfers until the necessary memory buffers become available to store the data and transfer it to a lower data rate capable target device.
Still another technical advantage of the present invention relates to its ability to process read/write commands from multiple Fibre Channel hosts to multiple targets devices. Such a streaming method and system provides the capability to queue commands from the same or other Fibre Channel hosts within the SCSI router interface so that subsequent commands are not lost while awaiting execution of a prior command.
A still further technical advantage of the present invention is that it provides command processing in a Fibre Channel-to-SCSI router interface without the cost and physical memory requirements of current command processing methods and systems while still providing increased performance and efficiency.
An even further technical advantage of the present invention relates to its ability to be made part of a Fibre Channel network with little additional cost. Generally, the method of the present invention may be implemented as a change in the instructions that control the processing of commands to a target device in a Fibre Channel network. These changes may be implemented in a hardware protocol chip for controlling the protocol operations within the network. Even this modification may be done with relatively little expense.